In the prior art, an antenna receiving system had a direction finding computer that controlled attenuators and signal phase shifters.
The disclosed antenna receiving system has both a direction finding computer and a beam forming computer. Each of the direction finding computer and the beam forming computer control the same signal attenuators and signal phase shifters.
The presently disclosed antenna receiving system has a direction finding computer. The direction finding computer can determine a direction to one or more moving vehicles that transmit right handed and left handed circularly polarized radiation. A method used by the direction finding computer is disclosed.
The beam forming computer of the antenna receiving system then forms a beam in each found direction. The antenna receiving system receives data from each located moving vehicle over the beam formed on that moving vehicle.
The presently disclosed antenna receiving system includes a hemispherical array of dual sense helical antenna elements. Such a dual sense helical antenna element is disclosed in U.S. Pat. No. 4,494,117. The teachings of U.S. Pat. No. 4,494,117 are incorporated herein by reference. Such a dual sense helical antenna element is also referred to as a dual sense helicone, or simply a helicone.
The direction finding subsystem of the disclosed antenna receiving system nearly simultaneously electronically computes an angle of arrival of dual circularly polarized radiation from each of one or more moving vehicles. The direction finding subsystem then electronically determines a direction for formation of a central receiving antenna beam for receiving data from each of the one or more moving vehicles.
In the direction finding phase, right hand polarized radiation is received by each helicone element. The right hand polarized radiation comes from each moving vehicle. The amplitude and phase of an electrical voltage output produced due to right hand polarized radiation received by each dual sense helicone is adjusted by an attenuator and a phase shifter under control of the direction finding computer. The value of the amplitude and value of the phase of the adjusted electrical voltage output are then measured by the direction finding computer.
Also, left hand polarized radiation is received by each helicone. The left hand polarized radiation comes from each moving vehicle. The amplitude and phase of an electrical voltage output produced due to left hand polarized radiation received by each dual sense helicone is adjusted by an attenuator and a phase shifter under control of the direction finding computer. The value of the amplitude and the value of the phase of each adjusted electrical voltage output are then measured by the direction finding computer. From measured values of amplitude and phase, the direction finding computer locates a direction to each of one or more moving vehicles, nearly simultaneously.
The disclosed antenna receiving system also has a beam forming computer. The beam forming computer also adjusts and measures the amplitudes and phases of electrical voltage outputs produced due to right hand and left hand polarized radiation received by the dual sense helicones of the antenna receiving system. The beam forming computer uses the measurements of amplitude and phase to electronically determine a combination of four helicones, that taken together, forms a complete high gain antenna receiving beam. Information, that is data, can then be received in dual circularly polarized radiation received by the high gain antenna receiving beam.
Two electrical voltage outputs are produced within each helicone of the antenna array of the electronically steered hemispherical antenna array system due to reception by each helicone of the right and left hand circular polarized radiation coming from each moving vehicle. The beam forming computer forms and points a complete receiving antenna beam in the direction of dual circularly polarized radiation coming from each moving vehicle.
A direction for a central portion of the complete antenna receiving beam to each of the moving vehicles, is initially determined by the direction finding computer. The beam forming computer maximizes signal-to-noise ratio at output terminals of four selected helicones of the hemispherical antenna array, to receive information carrying radiation from each of the moving vehicles. Such information is referred to as data coming from the moving vehicle.
The following cited publications are incorporated herein by reference. The publications are:
1. Paper entitled xe2x80x9cAn Electronic Scanned Dual-Polarized Antenna for Tracking Multiple Targets Simultaneouslyxe2x80x9d by W. Gregorwich et al., published as part of the 1994 IEEE Aerospace Applications Conference; and
2. Paper entitled xe2x80x9cElectronic Scanning Parabolic-Reflection Excited by a Cluster-Feed Arrayxe2x80x9d by W. Gregorwich et al., published as part of the 1995 IEEE Aerospace Applications Conference.
A first objective is to provide beamforming that ensures that the response of the antenna receiving system is smooth during electronically steered from one azimuth/elevation direction to another. To produce smoothness, the phase modulation of the beamformer output should be free from transient xe2x80x9cphase jumpsxe2x80x9d. The lack of smoothness is a problem suffered by a conventional switch network that are used for beamforming, resulting in loss of data(dropouts).
The second objective is to minimize the time needed by the antenna receiving system to steer its antenna beam from one direction to another.
The third objective is to minimize the amount of hardware, especially the number of phase shifters and antenna elements needed to implement the beamformer.
The forth objective is to enable the antenna receiving system to simultaneously track and receive data from a multiple number of moving vehicles by using the same beamforming network.
The fifth objective is to form antenna beams by using a multiple number of helicones, thus maximizing gain.
A prior art antenna receiving system might use PIN diode switches of a beamforming network to implement an antenna beam. Each additional antenna beam to be formed by the prior art antenna receiving system might use additional PIN diode switches of an additional beamforming network.
A prior art method of switching from one set of array elements to another set of array elements in a discrete fashion introduces transient phase jumps in the phase modulated signal at the output of a beamformer. Such jumps are not acceptable for most applications. Forming multiple beams is realized in a prior system by using multiple but independent beamforming networks. Such networks increase the weight, power consumption and complexity of the system.
The disclosed antenna receiving system allows a relatively small number of helicones, attenuators and phase shifters to form from two to four simultaneous receiving beams. This feature leads to smaller size and lighter weight.
The disclosed antenna system produces relatively low sidelobe levels below 15 degree elevation. This feature is important for multi-path mitigation.
The disclosed antenna system has a rapid and smooth beam steering response. This feature is important for the tracking of phase modulated telemetry signal without data dropout.
The disclosed antenna receiving system stores beamforming information in terms of the beam control byte values; thus, minimal time is required for beam steering during real time operation. The rapid formation of two independent beams, using the same beamforming network of attenuators and phase shifters, with no phase jump, is achieved. The implementation of the conjugate field matching solution is designed based on engineering judgment to give up a small amount in SNR to ensure the output of the beamforming subsystem produces a beam with a relatively low sidelobe level.
An antenna receiving system comprising an array of dual sense helical antenna elements for receiving right hand circular polarized radiation and left hand circular polarized radiation, each dual sense helical antenna element having a right hand circular polarized radiation signal output and having a left hand circular polarized radiation signal output, a set of right hand circular polarized attenuators and a set of left hand circular polarized attenuators, a right hand circular polarized attenuator connected to the right hand circular polarized radiation signal output of each dual sense helical antenna element and a left hand circular polarized attenuator connected to the left hand circular polarized radiation signal output of each dual sense helical antenna element, a set of right hand circular polarized phase shifters and a set of left hand circular polarized phase shifters, a right hand circular polarized phase shifter connected to a right hand circular polarized attenuator, and a left hand circular polarized phase shifter connected to a left hand circular polarized attenuator, a direction finding computer having a first output connected to an attenuation setting input of each of the set of right hand circular polarized attenuators, the direction finding computer having a second output connected to an attenuation setting input of each of the set of left hand circular polarized attenuators, the direction finding computer having a third output connected to a phase setting input of each of the set of right hand circular polarized phase shifters, the direction finding computer having a fourth output connected to a phase setting input of each of the set of left hand circular polarized phase shifters, a signal output of the set of right hand circular polarized phase shifters connected to the direction finding computer and a signal output of each of the set of left hand circular polarized phase shifters connected to the direction finding computer, and a beam forming computer having a first output connected to an attenuation setting input of each of the set of right hand circular polarized attenuators, the beam forming computer having a second output connected to an attenuation setting input of each of the set of left hand circular polarized attenuators, the beam forming computer having a third output connected to a phase setting input of each of the set of right hand circular polarized phase shifters, the beam forming computer having a fourth output connected to a phase setting input of each of the set of left hand circular polarized phase shifters, a signal output of the set of right hand circular polarized phase shifters connected to the beam forming computer and a signal output of each of the set of left hand circular polarized phase shifters connected to the beam forming computer.